What about Reveillark? I understand that i get the trigger twice with Teysa, because the leaves the battlefield trigger is caused by death. But let's say that i only have two creatures with power 2 or less in the graveyard when Reveillark dies, can i let one of the triggers resolve, sacrifice the two creatures that i get back, then let the second trigger resolve and get those two same creatures back?
No. If Reveillark's second ability triggers more than once, the abilities that trigger this way will go on the stack the next time a player would get priority (so before any one of them resolves), and that's when you choose targets separately for each Reveillark ability that goes on the stack this way (C.R. 603.3, 603.3d, 601.2c, 117.4). These targets can be the same or different. However, if you target the same card or cards this way and one Reveillark ability brings such a card to the battlefield, that card will be an illegal target for any other ability with targets (including the other Reveillark ability or abilities on the stack) (C.R. 608.2b) — this is true even if the permanent that card becomes returns to the graveyard before that other ability would resolve (C.R. 400.7). Therefore, in general, targeting the same card or cards this way will have little practical effect, if any. See also this thread and this thread.
EDIT (Mar. 11, 2020): One rule was renumbered with Core Set 2020.
EDIT (Mar. 11, 2020): One rule was renumbered with Core Set 2020.